Many of today's personal communication systems (PCS) operate at approximately 1.9 Gigahertz (GHz). Whip antennas are generally used in the portable communication devices of PCS, such as digital European cordless telephone (DECT). FIG. 1 of the accompanying drawings shows a partial cross sectional view of a prior art communication device 100 having a typical whip antenna 102. Included within the whip antenna 102 are half wavelength radiator 104 and base helical 106. The base helix 106 is electrically connected to a transceiver board (not shown) located within the radio housing 108 and capacitively coupled to the half wavelength parasitic 104. Two non conductive portions or gaps 110, 112 exist at either end of the half wavelength radiator 104. These non conductive portions 110, 112 are typically formed of plastic material. Half wavelength parasitic 104 and non conductive portions 110, 112 are usually overmolded with plastic forming an extendible and retractable radiator portion 114. The top non conductive portion 112 aligns with the base helix 106 when the radiator 114 is in the retracted position, thereby preventing the antenna 102 from becoming detuned. In the retracted position, the only portion of the antenna acting as a radiator is the base helix 106. The performance of the prior art communication device 100 with the radiator portion 114 in the retracted position and using only the base helix 106 is greatly degraded.
The typical half wavelength parasitic 104 including the surrounding plastic molding may be 6 centimeters long at frequencies of 1.9 GHz. Even though this is an effective radiator in free space, problems can arise when the extendible radiator portion 114 of whip antenna 102 is retracted into the housing. The only radiating part then becomes the base helix 106 which is normally short and in very close proximity to internal ground shields (not shown). These ground shields encase the transceiver and are located next to the internal surface of the housing 108. The signals received or transmitted at the base helix 106 create antenna currents across the shields (also known as case currents) next to the housing. The radiation performance in this situation is poor due to the case currents not being in phase within the base helix 106 currents. When the communication device 100 is in use, the housing 108 is substantially enclosed in the operator's hand resulting in a substantial reduction in radiation efficiency.
Since users of PCS devices typically carry the device in a pocket or carry case, they tend to carry the device with the antenna in the retracted position. This however, forces the user to extend the antenna every time he wishes to use the device or keep the antenna extended at all times. Hence, there is a need for an antenna configuration that allows user to use the PCS communication device without having to extend the antenna.